In industrial settings, control systems are used to monitor and control inventories of industrial and chemical processes, and the like. Typically, the control system performs these functions using field devices distributed at key locations in the industrial process and coupled to the control circuitry in the control room by a process control loop. The term “field device” refers to any device that performs a function in a distributed control or process monitoring system, including all devices currently known, or yet to be known, that are used in the measurement, control, and/or monitoring of industrial processes.
Typical field devices include device circuitry that enables the field device to perform conventional field device tasks such as process parameter monitoring and measurements using one or more sensors, and/or process control operations using one or more control elements. Exemplary sensors include pressure sensors, flow sensors, level sensors, temperature sensors, and other sensors used in industrial processes. Exemplary control elements include actuators, solenoids, valves, and other control elements.
The device circuitry of field devices may also include a controller that is used to control the sensors and/or control elements, and communicate with a process control room, or other circuitry, over a process control loop, such as a 4-20 mA process control loop, for example. In some installations, the process control loop is used to deliver a regulated current and/or voltage to the field device for powering the field device. The process control loop can also carry data, such as a process parameter value corresponding to a sensed process parameter. This data may be communicated over the process control loop as an analog signal, or as a digital signal.
When the field device is powered by the process control loop, it is typically designed to consume very little power. In order to provide other operations beyond those typically provided by the device circuitry, such as wireless data communications or flash writes, for example, field devices commonly have either a supplemental power supply, such as solar panels, or a bulk supply circuit (e.g., a battery or capacitor), that can power the circuitry that is used to perform such operations.
Bulk supply circuits in conventional field devices are conventionally trickle charged until they are capable of providing sufficient current to power the circuitry that is used to perform the operation. The trickle charging is set very slow to ensure that the device circuitry always has sufficient power to perform its process parameter monitoring or measuring, and/or process control functions. For example, when the bulk supply circuit is configured to charge a capacitor, the charging circuit is forced to have a fixed and long time constant to charge the capacitor that is limited to the worst-case power budget for the device circuitry. As a result, the bulk supply is charged very slowly even when excess power from the control loop is available that would allow for faster charging rates. Additionally, the frequency at which the field device can perform high-power operations is very low.
The low frequency at which supplemental operations may be performed can be problematic when it is necessary to perform several operations to complete a desired task, such as a wireless data communication. For example, due to the limited power available, a single wireless data communication may only transmit a small amount of data. Thus, for larger data amounts, it is necessary to perform several cycles of charging the bulk supply circuit, and discharging the bulk supply circuit to power the wireless communication circuitry. Due to the slow charging of the bulk supply circuit and the resultant low frequency at which the operations can be performed, a significant amount of time may be required to perform the data communication.